Strangely enough Enthronements in Europe are a pretty national affair. That is logical, of course, because it is about a new head of state and this is a business between the elected representatives of the nation and the new monarch.
Exception is the lavish Coronation ceremony in Britain which attracts lots of royals from outside the United Kingdom.
In Belgium there were no foreign royals when King Albert II was sworn in. In Luxembourg there was attention from Queen Beatrix (from the related House of Orange-Nassau, formerly ruling in Luxembourg) and from King Albert II (sister of the Grand Duchess and uncle to the new Grand Duke).
In the Netherlands there is a large royal crowd, but all of them are colleagues from the new Sovereign: Heirs and Heiresses or (when too young) other representatives. For an example in 1980 in Amsterdam were The Prince of Wales, The Crown Prince of Norway, The Prince of Liège, the Hereditary Grand Duke of Luxembourg and more. But no heads of state.
The most sober is, without doubt, Denmark: just an announcement by the Statsminister. And that was it.